Exhaust gas recirculation valve

ABSTRACT

A valve that constitutes part of an exhaust gas recirculation valve is connected to a shaft, such that the valve is rotatable together with the shaft in the interior of a main body. An outer peripheral surface of the valve is formed in a substantial spherical shape, the axis (center of curvature) of the valve and the axis of the shaft being arranged eccentrically by a predetermined distance along a flow direction of the exhaust gas. In addition, a percentage between the eccentric distance between the center of curvature of the valve and the axis of the shaft, and the diameter of a gas inlet port of the main body into which the exhaust gas flows is 5.5% or greater.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2012-068841 filed on Mar. 26, 2012, thecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust gas recirculation valve,which is capable of switching between fluid passages, and whereby anexhaust gas of an internal combustion engine is recirculated from anexhaust system to an intake system.

2. Description of the Related Art

Heretofore, an exhaust gas recirculation valve has been used, forexample, for eliminating harmful components that are discharged from aninternal combustion engine. Such an exhaust gas recirculation valve hasfunctions to communicate between the intake system and the exhaustsystem of the internal combustion engine for recirculating the exhaustgas, which has been discharged from the internal combustion engine, toan intake system, in order to reduce harmful components such as NOx orthe like contained in the exhaust gas.

In Japanese Laid-Open Patent Publication No. 2010-236686, the presentapplicant has proposed a fluid passage valve, which is disposed in anexhaust gas recirculation passage connected between an intake passageand an exhaust passage of an internal combustion engine. The fluidpassage valve includes a main body, which is connected to the exhaustgas recirculation passage, and having a spherical shaped ball valve,which is arranged rotatably in the interior of the main body. Inaddition, by rotating the ball valve, which is connected through a shaftto a rotary drive source, through a predetermined angle, a state ofcommunication is switched between an exhaust gas inlet port and anexhaust gas outlet port that are formed in the main body, whereby a flowthrough state of the exhaust gas into the exhaust gas recirculationpassage is controlled.

SUMMARY OF THE INVENTION

A general object of the present invention is to provide an exhaust gasrecirculation valve, which is capable of realizing a more linear flowrate characteristic of the exhaust gas, together with enabling anincrease in the flow rate of the exhaust gas.

The present invention is an exhaust gas recirculation valve including abody having a fluid passage through which an exhaust gas flows, a valvearranged in the fluid passage that switches a flow through state of theexhaust gas, at least a portion of an outer peripheral surface of thevalve being spherically shaped, a seat member having a seat section,which is disposed in the fluid passage on an upstream side from thevalve and on which the valve is seated, and a shaft connected to thevalve and which rotates the valve, wherein a percentage of aneccentricity amount between a center of curvature of the valve when thevalve is completely closed and an axis of the shaft along a direction offlow of the exhaust gas with respect to a diameter of an inlet portformed in the body and into which the exhaust gas flows is 5.5% orgreater.

According to the present invention, in an exhaust gas recirculationvalve having such a valve, in which at least a portion of an outerperipheral surface of the valve is spherically shaped, by setting theeccentric distance (offset distance) between the center of curvature ofthe outer peripheral surface and the axial center of the shaft such thatthe percentage thereof with respect to the diameter of the exhaust gasinlet port of the body into which the exhaust gas flows is 5.5% orgreater, the flow rate characteristic of the exhaust gas that flowsthrough the fluid passage can be made more linear, while also enablingthe flow rate of the exhaust gas to be increased.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which a preferredembodiment of the present invention is shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view shown partially in cross section of anexhaust gas recirculation valve according to an embodiment of thepresent invention;

FIG. 2 is a cross sectional view taken along line II-II of FIG. 1;

FIG. 3 is a characteristic line diagram showing a relationship betweenan eccentric distance between an axis of a shaft and an axis of thevalve along a direction of flow of the exhaust gas, and the flow rate ofan exhaust gas when the valve is completely open, in the exhaust gasrecirculation valve of FIG. 1;

FIG. 4A is a characteristic line diagram with respect to the exhaust gasrecirculation valve of FIG. 1, showing a relationship between theeccentric distance of the shaft and the exhaust gas flow rate when thevalve is completely open, for a case in which the diameter of a gasinlet port is small; and

FIG. 4B is a characteristic line diagram with respect to the exhaust gasrecirculation valve of FIG. 1, showing a relationship between theeccentric distance of the shaft and the exhaust gas flow rate when thevalve is completely open, for a case in which the diameter of a gasinlet port is large.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIGS. 1 and 2, an exhaust gas recirculation valve 10includes a main body (body) 12, a valve 14 disposed rotatably in theinterior of the main body 12, a valve seat (seat member) 16 with whichan outer peripheral surface of the valve 14 is in abutment (contact),and a drive force transmission mechanism 18 disposed in an upper portionof the main body 12 and which imparts a rotary drive force to the valve14.

The main body 12 is formed from a metallic material, for example. On thelower side of the main body 12, there are provided a gas inlet port(inlet port) 20 to which the exhaust gas is supplied, and a gas outletport 22 disposed on an opposite side from the gas inlet port 20 throughwhich the exhaust gas is directed out and circulated to an internalcombustion engine (not shown). In the main body 12, the gas inlet port20 and the gas outlet port 22 are disposed substantially on a straightline. Further, a communication chamber (fluid passage) 24 is formed inthe main body 12 between the gas inlet port 20 and the gas outlet port22, and the substantially disk-shaped valve 14 is arranged rotatably inthe interior of the communication chamber 24.

Between the communication chamber 24 and the gas inlet port 20, aninstallation opening 26 is formed, which is expanded in diameter withrespect to the gas inlet port 20. The valve seat 16, which slides on theouter peripheral surface of the valve 14, is disposed in theinstallation opening 26. The valve seat 16, for example, is formed froma metallic material, and is equipped with a communication hole 28 thatpenetrates therethrough in an axial direction (the direction of arrowsA1 and A2), and a tapered seat section 30, which gradually expands indiameter from the interior of the communication hole 28. In theinstallation opening 26, the communication hole 28 is arranged on theside of the gas inlet port 20 of the main body 12 (in the direction ofthe arrow A2), whereas the seat section 30 is arranged on the side ofthe communication chamber 24 (in the direction of the arrow A1). Inaddition, the gas inlet port 20 and the communication chamber 24 areplaced in communication through the communication hole 28 of the valveseat 16.

Further, the valve seat 16 is movably disposed in the installationopening 26 both in an axial direction (the direction of arrows A1 andA2) and in a radial direction. A spring 34 is interposed between thevalve seat 16 and a ring-shaped stopper 32 provided on the communicationchamber 24 side of the installation opening 26. The valve seat 16 isurged by the spring 34 toward the side of the gas inlet port 20 (in thedirection of the arrow A2).

On the other hand, as shown in FIG. 1, in a substantially centralportion of the main body 12, a shaft hole 36 is formed, which penetratesin a vertical upward direction from the communication chamber 24. Alater-described shaft 38 of the drive force transmission mechanism 18 isinserted through the shaft hole 36.

The valve 14 comprises a substantially disk-shaped main body portion 40having a hemispherical shaped outer peripheral surface, and an axialportion 42, which projects in the axial direction (the direction of thearrow A2) from an end of the main body portion 40 and is connected tothe shaft 38.

The drive force transmission mechanism 18 includes the shaft 38, whichis connected to the valve 14, a valve gear 44 connected to an upper endof the shaft. 38, and a drive source 46 connected to an upper part ofthe main body 12 and which drives the shaft 38 rotatably through thevalve gear 44.

The upper end of the shaft 38 is inserted through a substantiallycentral portion of the valve gear 44, and the shaft 38 is fixed to thevalve gear 44 by tightening a nut 48 thereon. In addition, the shaft 38is rotatably supported by a pair of bearings 50 a, 50 b, which aremounted in the main body 12 respectively above and below the valve 14.

Further, as shown in FIG. 2, the axis B1 of the shaft 38 is connected soas to be positioned eccentrically (i.e., offset) with respect to an axisB2 through which the center of curvature of the outer peripheral surfaceon the valve 14 when the valve 14 is completely closed passes. Morespecifically, the axis B1 is set to be parallel with the axis B2 of thevalve 14, and is separated therefrom by a predetermined distance.

For this reason, the valve 14 is arranged within the communicationchamber 24 so as to be rotatable (swingable) about the axis B1, which isset at a position eccentric (offset) from the axis B2.

The axis B1 of the shaft 38 is arranged so as to be eccentric withrespect to the axis B2 of the valve 14 by a predetermined distance(eccentric distance L) toward the downstream side (in the direction ofthe arrow A1) along the direction of flow of the exhaust gas.

More specifically, the percentage of the eccentric distance L withrespect to the diameter D of the gas inlet port 20 in the main body 12is set to be equal to or greater than 5.5% (L/D×100≧5.5). Statedotherwise, the value obtained by dividing the eccentric distance L bythe diameter D is equal to or greater than 0.055.

The drive source 46 is constituted, for example, from a stepping motoror a rotary actuator, which is driven rotatably by supply of electriccurrent thereto. By transmitting the rotary drive force of the drivesource 46 to the shaft 38 via the valve gear 44, the valve 14, which isconnected to the shaft 38, is moved or actuated rotatably about the axisB1.

The exhaust gas recirculation valve 10 according to the embodiment ofthe present invention is constructed basically as described above. Next,operations and advantages thereof shall be explained. A valve-closedstate, as shown in FIGS. 1 and 2, will be described as an initialposition, in which the outer peripheral surface of the valve 14 isseated on the seat section 30 of the valve seat 16, and communicationbetween the gas inlet port 20 and the gas outlet port 22 is blocked.

From the initial position, which is the valve-closed state as describedabove, by driving the drive source 46 of the drive force transmissionmechanism 18, a rotary drive force of the drive source 46 is transmittedto the shaft 38 through the valve gear 44. The shaft 38 rotates thevalve 14, which is connected to the shaft 38, counterclockwise apredetermined angle about the axis B1, which is located at a positioneccentric (offset) from the axis B2. Consequently, the valve 14 isdisplaced in a direction to gradually separate away from the valve seat16.

In addition, as a result of the outer peripheral surface of the valve 14separating away from the seat section 30 of the valve seat 16, avalve-open state is brought about, and the exhaust gas, which issupplied to the gas inlet port 20 through a gap between the outerperipheral surface and the seat section 30, is introduced to theinterior of the communication chamber 24. By further rotation of thevalve 14 under a driving action of the drive source 46, the valve 14 isgradually separated away from the seat section 30, whereby a fullyvalve-open state is brought about in which the valve 14 is rotated fromthe initial position, for example, by about 90°.

In the valve-open state, the exhaust gas supplied to the gas inlet port20 flows through the communication hole 28 of the valve seat 16, passesthrough the communication chamber 24, and then flows to the gas outletport 22, whereupon the exhaust gas is supplied to a non-illustratedinternal combustion engine.

Next, with reference to FIGS. 3, 4A and 4B, explanations shall be givenof the relationship between the diameter D of the gas inlet port 20 inthe main body 12, the eccentric distance L, and the flow rate at a timeof full opening when the valve 14 is in a fully open state.

FIG. 3 is a characteristic line diagram showing a relationship betweenthe eccentric distance L and the flow rate of the exhaust gas when thevalve 14 is completely open, for a case in which the diameter D of thegas inlet port 20 is 18 mm. FIG. 4A is a characteristic line diagramshowing a relationship between the eccentric distance L and the flowrate of the exhaust gas, for a case in which the diameter D of the gasinlet port 20 is 9 mm and thus is smaller in diameter than theaforementioned gas inlet port 20 of FIG. 3. FIG. 4B is a characteristicline diagram showing a relationship between the eccentric distance L andthe flow rate of the exhaust gas, for a case in which the diameter D ofthe gas inlet port 20 is 27 mm and thus is larger in diameter than theaforementioned gas inlet port 20 of FIG. 3.

First, from the characteristic line diagram shown in FIG. 3, it can beunderstood that, from a condition in which the eccentric distance L isnonexistent (L=0) until the eccentric distance L reaches in theneighborhood of roughly 1 mm, the flow rate of the exhaust gas increasesrapidly, and then as the eccentric distance L becomes equal to andexceeds 1 mm, the rise in the flow rate slows down or levels off. Statedotherwise, the rate of change at which the flow rate of the exhaust gasincreases continues to rise and becomes greatest when the eccentricdistance L reaches about 1 mm. More specifically, the flow ratecharacteristic undergoes a change in the vicinity of where the eccentricdistance L is about 1 mm.

For this reason, since the increase in the flow rate of the exhaust gascontinues to become larger until reaching an eccentric distance L atwhich the percentage (L/D×100) between the diameter D of the gas inletport 20 and the eccentric distance L is roughly 5.5%, at least thepercentage of the eccentric distance L with respect to the diameter D ofthe gas inlet port 20 should be set to 5.5% or greater.

Further, from the characteristic line diagram shown in FIG. 4A, it canbe understood that, from a condition in which the eccentric distance Lis nonexistent (L=0) until the eccentric distance L reaches in theneighborhood of roughly 0.5 mm, the flow rate of the exhaust gasincreases rapidly, and then as the eccentric distance L becomes equal toand exceeds 0.5 mm, the rise in the flow rate lessens and rises moreslowly. More specifically, the flow rate characteristic undergoes achange in the vicinity of where the eccentric distance L is about 0.5mm. In this case as well, the relationship between the eccentricdistance L and the diameter D of the gas inlet port 20 is such that0.5/9×100≈5.5%.

Furthermore, from the characteristic line diagram shown in FIG. 4B, itcan be understood that, from a condition in which the eccentric distanceL is nonexistent (L=0) until the eccentric distance L reaches in theneighborhood of roughly 1.5 mm, the flow rate of the exhaust gasincreases rapidly, and then as the eccentric distance L becomes equal toand exceeds 1.5 mm, the rise in the flow rate lessens and rises moreslowly. More specifically, the flow rate characteristic undergoes achange in the vicinity of where the eccentric distance L is about 1.5mm. In this case as well, the relationship between the eccentricdistance L and the diameter D of the gas inlet port 20 is such that1.5/27×100≈5.5%.

In the foregoing manner, according to the present embodiment, in anexhaust gas recirculation valve 10 in which the center of curvature(axis) B2 of the valve 14 and the axis B1 of the shaft 38 that rotatesthe valve 14 are eccentric, by setting the relationship between thediameter D of the gas inlet port 20, which is formed in the main body 12and through which the exhaust gas flows into the main body 12, and theeccentric distance L between the center of curvature (axis) B2 of thevalve 14 and the axis B1 of the shaft 38 along the flow direction of theexhaust gas, such that the eccentric distance L is 5.5% or greater thanthe diameter D, the flow rate characteristic of the exhaust gas can bemade more linear, while the flow rate of the exhaust gas can also beincreased.

The exhaust gas recirculation valve according to the present inventionis not limited to the above-described embodiment, and it is a matter ofcourse that various additional or modified structures could be adoptedtherein without deviating from the essential gist of the presentinvention.

What is claimed is:
 1. An exhaust gas recirculation valve comprising abody having a fluid passage through which an exhaust gas flows, a valvearranged in the fluid passage that switches a flow through state of theexhaust gas, at least a portion of an outer peripheral surface of thevalve being spherically shaped, a seat member having a seat section,which is disposed in the fluid passage on an upstream side from thevalve and on which the valve is seated, and a shaft connected to thevalve and which rotates the valve, wherein a percentage of aneccentricity amount between a center of curvature of the valve when thevalve is completely closed and an axis of the shaft along a direction offlow of the exhaust gas with respect to a diameter of an inlet portformed in the body and into which the exhaust gas flows is 5.5% orgreater.